This invention relates to a process for alkylating naphthalene with olefins. More particularly, this invention relates to a process for producing a mixture of isopropylnaphthalenes from naphthalene and propylene in the presence of sulfuric acid.
The alkylation of aromatic compounds with alkylating agents in the presence of sulfuric acid as a catalyst to produce higher molecular weight alkylation products has been known in the art for some time. Alkyl arenes are produced by the alkylation of arenes like benzene, naphthalene, anthracene and other fused-ring aromatic compounds with alkylating agents like olefins, or borate esters or sulfones, or alkyl ethers in the presence of sulfuric acid. If acid strength is sufficient, alkylation and sulfonation occur simultaneously and alkyl aromatic sulfonic acids are produced. The sulfuric acid strength is sufficient when the amount of sulfuric acid is a stoichiometric excess over the amount of aromatic compound. When an olefin is used the ratio of olefin to aromatic compound is at least 2 to 1.
Condensation products of naphthalene are produced by treating the naphthalene with sulfuric acid and olefins. The naphthalene and sulfuric acid react to produce a mixture of alpha and beta naphthalene sulfonic acids. This mixture is caused to react with a mixture obtained by passing propylene and other high molecular weight olefins into concentrated sulfuric acid. The ratio of olefin to naphthalene should be 2 to 1. The temperature must not exceed 100.degree.C. The amount of sulfuric acid is kept at such a high value that it limits the tendency of the olefins to hydrolyze to alchols in the presence of water. The condensation product is purified by being insoluble in water or by precipitation with a strong sulfuric acid. The condensation product may be further purified by treatment with lime and soda which produces the alkali metal salts of the sulfuric acids as the condensation products.
A mixture of monosubstituted and polysubstituted isopropylnaphthalenes is used as a solvent for use in the coatings industry, for use as a low temperature heat transfer solvent, for use as a gasoline and petroleum additive, and for use as a solvent for dyes in chemical microencapsulation processes.
The object of this invention is to provide a process for the production of a mixture of monosubstituted and polysubstituted isopropylnaphthalenes by the use of an insitu prepared catalyst.